Various types of laser beam scanning apparatus are known. In flat bed scanners, a sheet to be scanned, which may be rigid and formed of a material such as glass or metal, or flexible and formed of a material such as film or paper, is arranged in a planar orientation. In drum scanners, the sheet to be scanned is flexible and is arranged in a cylinder.
In state of the art scanners, the flexible object to be scanned is rigidified by a cylindrical member or drum of similar dimensions which is positioned either radially outward (in internal drum scanners) or radially inward (in external drum scanners) of the object to be scanned. In both instances, adjustments must be made for the thickness of the object to be scanned. In external drum scanners, if the area to be scanned is large, the external drum is large and consequently, bringing the drum up to operating speed and subsequently slowing the drum when operation is terminated, are both time-consuming. Also, autoloading of sheets to be scanned is difficult to implement.
U.S. Pat. No. 4,684,228 to Holthusen discloses a transparent cylindrical rigidifying member or drum which supports a sheet on its outer surface, emulsion side inward, such that a spinner may translate along the axis of the drum and scan the sheet. This apparatus enables scanning to take place generally without adjusting for thickness of the sheet. However, the drum must be formed of high quality optical material, which is relatively expensive, so as not to introduce artifacts.
Early patents on internal drum scanners include the following:
A. U.S. Pat. No. 2,394,649 to Young describes a very early internal drum scanner having a 180 degree working area.
B. U.S. Pat. No. 2,253,799, also to Young, describes a facsimile system having a rotating scanner moving longitudinally within a stationary transparent drum. The system includes a directly coupled read/write system.
C. U.S. Pat. No. 3,739,088 to Landsman relates generally to a printing sheet production method and apparatus. The printing sheet is described in detail. The printing sheet production apparatus is described briefly at lines 19-26 of column 5.
D. U.S. Pat. No. 3,816,659 to Landsman describes internal drum scanning apparatus in which the substrate to be scanned is arranged radially inward of a conventional tube-like construction. The scanning mirror is inclined at a 52.5 degree angle, rather than at a 45 degree angle.
In a presentation at the Electro 79 Conference (Apr. 24-26, 1979, New York), published in 1979 in the form of an article in the conference record entitled "Laser platemaking", Robert M. Landsman of Log Etronics, Inc. described an internal drum opto-mechanical scanner which is designed to function both as a reading device and as a writing device. The scanner comprises a single faceted rotating mirror which is air turbine actuated. The Landsman scanner has flat-bed type loading of the substrate (paste-ups to be scanned or sheets to be imaged) in which a carrier resembling a roll top desk cover transforms the configuration of the substrate from planar to cylindrical.
Similar apparatus is described in Landsman, R. M., A Laser Imaging System for Plate Making and Facsimile, SPIE, Vol. 223, pp. 2-6. The system described may load a single sheet having a prespecified size such as 17".times.24", in which case sheet support discs rotate 180 degrees, or two sheets of the same size, in which case the sheet support discs rotate 360 degrees.
U.S. Pat. No. 4,131,916 to Landsman describes a pneumatically actuated image scanning reader/writer system. As described therein (col. 2, line 46), "(t)he opto-mechanical portion of the system is comprised of three major components, each of generally cylindrical configuration, namely a copy reading station 25, a pneumatically-actuated scanning drive system 10 and an image writing station 28, all of which are assembled in horizontal end-to-end relationship and aligned about a single mechanical and optical axis."
The image writing station is briefly described at lines 45-58 of column 5: "At image writing station 28, the stationary circular end sheets 30, 31 by means of which the edges of a flexible sheet of image receptive material 29 are retained, aligned and supported to form either a partial or complete cylinder, are each provided with a central, circular aperture through which scanning member 14 is free to translate during operation of the apparatus. It would, of course, be possible to automate the loading and unloading of copy sheet 102 and/or image receiving sheet 29, and to provide a capability for simultaneously accommodating more than one such sheet in each station. . . ".
U.S. Pat. No. 4,511,205 to Crane describes a scanning system having a rotatable, axially translatable scanning beam. The patentee states that his scanning system is an improvement of the scanning system described in above-referenced U.S. Pat. No. 4,131,916 and specifically states that his invention "simply provides improved apparatus for translating and rotating the scanning mirrors". The improvement is stated to reside in the provision of a hollow shaft which carries the scanning mirror. Pressurized air is fed into the interior of the shaft and escapes through a turbine which rotates the shaft. The shaft is supported by air bearings from a surrounding housing and the housing is supported by a slide pneumatically supported from a stationary rail. The slide is translated parallel to the axis of the shaft by a lead screw driven by a stepping motor in cooperation with a lead screw nut affixed to the slide.
Polygonal spinners are reviewed in R. J. Sherman, "Polygonal scanners", in Laser Beam Scanning, G. F. Marshall (Ed.), Marcel Dekker, N.Y., USA, 1985. State of the art spinners are also described in U.S. Pat. Nos. 4,433,894 to Hanson et al, 4.475,787 to Starkweather and 4,853,709 to Stein et al.
Use of more than one scanning beam for scanning a photosensitive film is known for external drum and flat bed scanners. Methods for generating a plurality of scanning beams and employing them in external drum and flat bed applications are described in the following documents, the disclosures of which are incorporated herein by reference:
Technical Report #384, issued in August, 1978 by Isomet Corporation, P.O.B. 1634, Port Royal Rd., Springfield, Va., USA, and entitled: "Technical report on multibeam laser scanning";
"Applications of multi-beam acousto-modulators in laser-electrophotographic printing and drawing machines", Tokes, S. B., SPIE Proceedings No. 397, 1983;
U.S. Pat. No. 4,577,932 to Gelbart; and Hornbeck, L. J. "Deformable-mirror spatial light modulators", SPIE Critical Reviews Series, Vol. 1150, 1988, pp. 86-102.
Commonly used spinners are also described in the Detailed Description below with reference to FIGS. 23 to 25.